1. Field of Invention
This invention relates to traffic-control signs, specifically supplemental warning signs, usually bearing the message "STOP", that are used to back-up traffic signals that have been disabled by a power failure.
2. Description of Prior Art
A number of devices intended to supplement a disabled traffic signal in the event of a power failure are known in the related art:
In U.S. Pat. No. 3,863,214, Kerr, Jr. describes a supplemental visual display that cooperates with the operational mode of a traffic signal. The device is mounted to the back-side of a traffic signal housing and includes an arm that supports a visual display at one end and is rotatably secured to the shaft of an electric motor at its other end. An electromagnet is used to retain the arm in a normally upward position so that the visual display is hid behind the traffic signal housing. During a power failure, the electromagnet is released and a spring plunger assists the downward free fall of the arm so that the display is shown along the side of the traffic signal. Restoration of power causes the motor to raise the arm back to its original position where the arm contacts a normally closed switch that disconnects power to the motor.
In U.S. Pat. No. 4,642,605, Karp describes a power failure responsive warning device mountable to the side of a traffic signal housing. The device includes an arm pivotally mounted to a frame member and normally retained in an upright non-warning mode position by an electromagnet, such that the arm and frame member enclose a collapsible warning sign. Power interruption causes the electromagnet to release the arm so that the arm downwardly pivots away from the frame so as to unfold the collapsible sign. The device provides no mechanism for automatically returning the sign to the original non-warning position. Instead, the free end of the arm includes a reset plate that accepts the end of a hand-held pole in order to manually return the sign to its original position. To prevent unlatching of the arm during a momentary power glitch, the device includes a time delay circuit connected to the electromagnet.
In U.S. Pat. No. 5,504,481, Wys describes a fail-safe stop light apparatus that covers the face of a traffic signal with a warning sign as a result of a power failure. The device includes two members, each rotatably mounted to opposites sides of the traffic signal. Two electromagnets are used to retain each member in a first position away from the face of the traffic light. The electromagnets release the members during a power failure and two coil springs cause the members to rotate to a second position covering the face of the traffic light. An electric motor communicates with two linkage mechanisms to rewind the members to the original first position upon resumption of electrical power. A shut-off means, such as a switch or timer, is used to stop the motor once the members have been sufficiently rotated.
Actual field usage of the above-mentioned devices has not been obvious. Instead, the device most commonly used in the field to supplement a disabled traffic signal is the folded mechanical device shown for reference purposes in FIGS. 1A and 1B of the attached drawings. The device is usually mounted to the same pole used by the traffic signal and located below the traffic signal, so as to be accessible to a standing person. In some cases, the device may be mounted to a nearby support structure, such as a street light pole, which is in close proximity to the traffic signal. The device usually consist of two symmetrical halves of a typical stop sign that are connected together by a hinge mechanism. One sign half is usually fixed (mounted) to the traffic signal support pole and the other half is movable. Under normal conditions, the movable half of the sign is folded over the fixed half of the sign so as to not display the "STOP" message. Usually, there are matching holes or slots in the two sign halves to accept a padlock, or a hasp-type component which then accepts a padlock, in order to prevent tampering and limit access to the proper authorities, such as police or government officials. In order to display the "STOP" message using this device, an authorized individual manually unlocks the padlock, unfolds the two sign halves, and secures the sign in the open position (usually with a hasp-type component and padlock). This process is reversed in order to return the device to the normal folded position. An optional smaller message is sometimes affixed to the back of the movable half of the sign and is displayed when the sign is in the folded position.
Numerous disadvantages become apparent in the above detailed descriptions of the related art. The folded mechanical device, presumably popular because of its simplicity and ease of installation, has the major disadvantage of being manually activated. This manual activation can result in significant delays before the warning message is deployed and/or retracted, creating dangerous situations at traffic intersections. Although Kerr, Jr. and Wys present devices which activate automatically, the deployment methods are somewhat cumbersome, each device requires more than one electromechanical/magnetic component, including an electric motor with switch means to retract the warning message, and installation of the device requires modification to the traffic signal housing. Although Karp presents a device that does not use a motor or switch means, the resultant device is only semi-automatic, requiring the warning message to be manually retracted as in the case of the folded mechanical device. Karp's device also requires the added delay circuit to prevent nuisance deployment of the warning message, and installation requires modification to the traffic signal housing. All of the above-mentioned devices have working components that are exposed to the outside weather elements such as wind, rain, snow, ice, and corrosive elements like road salt, possibly causing damage to the device and/or hindering its movement. Karp acknowledges that modifications may need to be made to the collapsible sign to minimize the possibility of damage due to wind gusts. The hinge component and padlock used on the folding mechanical device are often seen to be rusted. The devices having exposed components are also subject to possible tampering, as is evident by the need for the padlock on the folding mechanical device.